1. Field of the Invention
The present invention relates to an electromotive stage for a microscope, disposed in an optical microscope, for electrically moving an observation object in two dimensions.
2. Description of the Related Art
For a conventional electromotive stage, a technique (first conventional example) is disclosed as a “microscope with an automatic sweeping apparatus” in Jpn. UM Appln. KOKAI Publication No. 59-53319. The first conventional example will be described with reference to FIGS. 27 and 28. In FIG. 27, an X-axis movement mechanism 501 and Y-axis movement mechanism 502 are disposed on a stationary stage 511 of the electromotive stage, so that a sample 512 can two-dimensionally be scanned with respect to an optical axis of a microscope. The X-axis movement mechanism 501 and Y-axis movement mechanism 502 are constituted of a movable base 503, a kremmel 504, ball screws 505, 506, and flexible cables 507, 508 shown in FIG. 28, and stepping motors 509, 510 shown in FIG. 27. Since the ball screws 505, 506 and flexible cables 507, 508 can transmit a rotary motion without any jounce, rotation angles of the stepping motors 509, 510 are accurately transformed into a linear motion of the movable base 503 or the kremmel 504. This constitution can realize a high precision stage without any lost motion.
Similarly, a technique (second conventional example) is disclosed as the “microscope with the automatic sweeping apparatus” in Jpn. UM Appln. KOKAI Publication No. 61-68219. Since the constitution of the microscope is substantially similar to that of the first conventional example, the description thereof is omitted. A mechanical power from a motor is transmitted to a rack disposed in the kremmel via a train of gears including a clutch. When the clutch is controlled, manual and electromotive operations can easily be switched, and an operationality of an electromotive microscope is enhanced. The mechanical power is transmitted using the train of gears, not the ball screws.
Moreover, a technique (third conventional example) is disclosed as a “stage for the microscope” in Jpn. Pat. Appln. KOKAI Publication No. 2000-214390. The third conventional example will be described with reference to FIGS. 29 and 30. In FIGS. 29 and 30, the stage has two members moved with respect to each other, such as a stationary base 601 and a movable base 602. In the one member a wire rope 604 is extended. In the other member a pulley 603 is disposed on a driving handle shaft. An urging member 605 applies a tensile force to the wire rope 604. Therefore, unless an abnormal operation, such as an operation of adding the overload higher than the frictional force between the pulley 603 and wire rope 604, is performed, the mechanical power is transmitted without any slip.
Furthermore, a technique (fourth conventional example) is disclosed as a “micro dimension positioning apparatus” in Jpn. UM Appln. KOKOKU Publication No. 4-22251. In the fourth conventional example, a photo interrupter sensor is used as a sensor for detecting an origin. The photo interrupter sensor has light emitting element and light receiving element which are disposed U-shaped housing. The elements are located in two opposed arms of the housing, respectively. An interrupting member inserted between the opposed arms interrupts light to the light receiving element from the light emitting element, and then an output signal is obtained. The photo interrupter sensor is inexpensively available. Here, a sensor optical axis refers to an optical axis connecting the light emitting element and the light receiving element. A position of the interrupting member to the sensor optical axis, where the interrupting member interrupts the light, is obtained, is not constant. A dispersion of the position is several tens of micrometers. That is, a precision with which the position of the member is detected is several tens of micrometers.
In general, an origin detection precision of about several micrometers is required in the electromotive stage for the microscope. Therefore, as long as the photo interrupter sensor directly detects the movement of the movable member, the required origin detection precision cannot be obtained. In the fourth conventional example, a micrometer for accurately transforming the rotary motion of a screw to a linear motion of a nut is used as a transmission means for transmitting the rotation of the motor to the movable member. Then, the photo interrupter sensor detects the rotation direction of the micrometer, and the movable member is positioned based on the signal of the sensor. Thereby, the origin detection precision of about several micrometers is realized.
In the second conventional example, the ball screw is not used, and a rack & pinion is used. Therefore, by a backlash of the gear, a moving distance differs in a case of moving in the same direction as the previous direction, and a case of moving in an opposite direction. That is, a lost motion is generated. Therefore, a high precision electromotive stage cannot be realized.
In the third conventional example, the wire rope is used. The wire rope is not applied to the electromotive stage.
In the fourth conventional example, a tensile spring is used to connect the micrometer to the movable member without any gap. Reduction of a change of an acting force of the spring in a movement range of 50 mm or more, necessary for the microscope, is incompatible with reduction of a space occupied by the tensile spring, and it is impossible to realize both reductions. Moreover, if the origin detector of the fourth conventional example is applied to the power transmission mechanism with the wire rope, a sensor detecting the position of the movable member in the moving direction and a sensor detecting the rotation position of the stepping motor in the rotation direction are required. However, since a slip is generated between the wire rope and the pulley, the rotation position of the output shaft of the stepping motor in the rotation direction dose not always synchronize with the position of the movable member to a stationary member. In the fourth conventional example, a method of setting the origin in the electromotive stage using the wire rope with high precision is not proposed.